Experimental and Numerical Study of Macro-Cell Corrosion Between Crossed Steel Bars

Reinforcing steel bars embedded in concrete are always intersected with each other to form rebar mesh or three-dimensional steel cage. The present study aims to investigate the phenomenon of severe corrosion observed at stirrups or some intersections of steel rebar mesh, which has not been well studied before. Macro-cell corrosion between crossed steel bars was considered to be the major cause for this phenomenon. In this regard, crossed steel bars were divided into intersected zone (IZ) and non-intersected zone (NIZ). The macro-cell current at the face-to-face IZ was calculated by Ohm’s law. A one-dimensional model based on transmission line method was employed to obtain the distribution of macro-cell current on the NIZ juxtaposed to the IZ. Experiments of steel bars in aqueous solutions and concrete were undertaken to verify the numerical model. The results demonstrated a good match between experiments and numerical model. It was also shown that the distribution of macro-cell current on the non-intersected areas was influenced by the resistivity of electrolyte. Based on the corrosion rate model presented in this study, the severe corrosion observed at stirrups or some intersection zones of rebar mesh can be explained and quantified

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Deterioration model of RC beams under marine atmospheric environment

This paper primarily proposes a deterioration model of reinforced concrete (RC) beams under marine atmospheric environment. Considering factors including corrosion initiation time, corrosion rate, corrosion non-uniformity and its effects on mechanical performances of steel bars, a comprehensive model was developed for the assessment of mechanical behaviour of RC beams under marine atmospheric environment. Also, to avoid the shortages brought by the classical truss theory, a modified compression field theory (MCFT) was applied to evaluate the effects of stirrups corrosion on the shear capacity of an RC beam. Then, according to a virtual case, the life-cycle performance of an RC beam was predicted through probability density evolution method (PDEM). Results approved the feasibility and effectiveness of the proposed model. Finally, further study work was pointed out

Macrocell corrosion between crossed steel rebars embedded in concrete under chloride environments

Steel reinforcement corrosion is found to be more severe at stirrups or some intersection zones of steel rebar mesh in concrete structures subjected to chloride penetration. This can be caused by macrocell corrosion formed between steel rebars with different potentials. Such potential differences are usually contributed by 1) chloride concentration gradients during the penetration process and 2) material differences between crossed steel rebars. With the forming of macrocell corrosion, the anodic current of steel with more negative potential will increase. The present study aims to deal with the macrocell corrosion between crossed steel macro-couples by dividing the steel rebar into intersected zone (IZ) and non-intersected zone (NIZ). The distribution of macrocell current on the surfaces of NIZ was obtained by means of a transmission line model. Based on the calculated macrocell current, the influence of the macrocell corrosion on the service life of reinforced concrete (RC) structures was analyzed. The results showed that the coupled micro- and macro-cell corrosion of stirrups could accelerate the change of the failure mode of a beam from bending to shear failure when the macrocell corrosion rate was no less than the microcell corrosion rate

A unified bond-slip model for the interface between FRP and steel

The interfacial bond-slip relationship between fiber-reinforced polymer (FRP) and steel plays an important role in analyzing FRP retrofitted steel structures. Different failure modes and epoxy types (i.e., linear epoxy and nonlinear epoxy) lead to various bond-slip relationships. Although several models have been proposed to predict the bond-slip behavior, different models were developed for different emphasis, which may result in inconve nience when being used. This paper proposed a unified bond-slip model by considering different failure modes and epoxy types. A database of bond strength comprising of 400 FRP-to-steel single-/double-lap shear joints was collected. By analytical reasoning, key factors that influence the bond parameters were identified and configu rations of the model were derived. The unknown coefficients in the model were determined subsequently by nonlinear regression analysis using the derived closed-form analytical solutions. Different coefficients were proposed in terms of different failure modes and epoxy types. Furthermore, if the failure modes are unknown before experimental investigation, the proposed model is also capable of giving reasonable predictions. Com parison between theoretical results and test data from the literature was performed to validate the modeling work. Afterward, a parametric study was conducted to further investigate effects of the key parameters on the interfacial behavior

A boundary element analysis of fatigue crack growth for welded connections under bending

Transverse fillet welded joints and circular hollow section (CHS)-to-plate welded connections were analyzed to obtain crack growth life under bending. Based on a 3D boundary element model, an initial semi-elliptical surface crack was embedded at the weld toe. Thereafter, crack propagation was performed with Paris’ law and strain energy density criterion. This method discards the assumption of constant aspect ratio of crack shape during propagation stage. Numerical results were compared with the experimental results in the literature. It is found that numerical analysis is reliable and the boundary element method is suitable for estimating the fatigue crack growth life

Probability Distribution of Cross-sectional radius of Corroded Steel Bars in Concrete and Its application

The impress current method is applied to acquire corroded steel bars embedded in concrete, and three-dimensional(3D) laser scanning techniques are applied on corroded steel bars to obtain the cross-sectional radius of corroded steel bars. Statistical analysis shows that with the increase of corrosion degree, the variation of radius of corroded steel bars increases linearly. For different types of steel bars, plain round steel bars have a larger sensitivity to corrosion than ribbed ones. Original radius of steel bars and mixture proportion of concrete have negligible effect on the variability of radius of corroded steel bars. A normal distribution model is obtained to describe radius data of corroded steel bars. For the convenience of practical application, the indicator, R, which is the ratio of the average to the minimum cross-sectional areas of corroded steel bars, is introduced to quantify the longitudinal variation of the cross-sectional areas. By using Monte-Carlo simulation, the indicator, R, of corroded steel bars are achieved based on the probability distribution of radius. The indicator R can be fitted well by the Gumbel distribution, and the distribution parameters increase linearly with the increases of corrosion degree

A boundary element analysis of fatigue crack growth for welded connections under bending

Transverse fillet welded joints and circular hollow section (CHS)-to-plate welded connections were analyzed to obtain crack growth life under bending. Based on a 3D boundary element model, an initial semi-elliptical surface crack was embedded at the weld toe. Thereafter, crack propagation was performed with Paris’ law and strain energy density criterion. This method discards the assumption of constant aspect ratio of crack shape during propagation stage. Numerical results were compared with the experimental results in the literature. It is found that numerical analysis is reliable and the boundary element method is suitable for estimating the fatigue crack growth life

Confinement of Masonry Columns with Steel and Basalt FRCM Composites

The rehabilitation of existing masonry elements by means of jacketing of columns using composite materials is becoming a remarkable technique in several applications that aim to increase the strength of existing masonry buildings. Fiber reinforced cementitious matrix (FRCM) composites are a newly developed strengthening system that consist of high-strength fibers embedded in a cementitious grout and externally bonded to the substrate. High resistance to fire and high temperatures, ease of handling during application, and vapor permeability with the substrate are some of the characteristics that make FRCMs a promising alternative to traditional organic composites such as fiber reinforced polymer (FRP) composites. This work presents the results of an experimental study carried out to understand the behavior of masonry columns with a square cross-section confined by steel and basalt fiber sheets embedded in a mortar matrix subjected to monotonic concentric compressive load. The effectiveness of the confinement is studied in terms of load-bearing capacity with respect to unconfined columns. The effect of corner radius for columns confined with basalt fibers is investigate